GM Titleblock Vertical Number

[maxmojo]

What is the intent of this number on a GM titleblock? I say it is the parent number of the drawing,
others seem to think it is the current number and rev level, only in vertical orientation.

 

[CoryPad]

Probably something to do with microfilm or microfiche storage of old drawings.

 

[desertfox]

I doubt its anything to do with the rev level because right next to the number you have highlighted it says rev 2 in the box.

 

[BrianE22]

Maybe the /001 means "page 1".

 

[tbuelna]

It's a legacy thing from when hardcopies of large format drawings were stored rolled.